WU concrete + flush-mounted boxes in the residential basement - how can this be solved?

Diffusion-proof? Oh dear, I have already read several times that a WU concrete basement massively releases moisture inside, which is precisely why we were instructed to install one decentralized fan per room.

Against earth, it’s hard to “breathe” anyway.

I think it makes sense to build the interior walls. Then, in the worst case, you have two walls in the room made of concrete, which cannot or should only be fitted with flush-mounted boxes with tricks (such as cladding, etc.).

You mean just a layer of bricks in front? 6 cm thick would be quite good, that would be ideal for 45mm flush-mounted boxes. But how do you connect it on the backside to the concrete wall?

WU basements with this wall thickness are diffusion-tight.

Yes, they are. However

In WU structures, diffusion slows down over time in the drying-out area and practically comes to a halt after releasing the internal moisture [5], [12]. Also, in [14], no cases of increased humidity were reported with constantly pressing water (floating houses).

In other words, with cast-in-place concrete it takes a while for the wall to dry through to the core.



There is quite a detailed information sheet on the topic "Waterproof concrete structures"—just google it.

And that’s why even shallow underfloor installations are not a good idea. Because you quickly get below the mandatory 200mm. The dowel only needs to have not removed the centering drill bit beforehand...

I am now assuming that the basement walls are 'normally' plastered

Assumption or part of the construction specifications?

Diffusion-proof? Oh dear, I have already read several times that a WU concrete cellar emits a lot of moisture inwardly; that’s exactly why we were instructed to install a decentralized fan in each room.



You mean just a layer of bricks in front? 6cm thick would be quite good, then it would be ideal for 45mm flush-mounted boxes. But how do you connect that on the back to the concrete wall?

No, I just mean that the exterior walls of the cellar made of concrete (precast or cast in place, doesn’t matter) would be built into the interior walls. Then you run the cables flush-mounted normally in the interior walls and save yourself the hassle with cladding and so on.

Yes, they are. However, with in-situ concrete it takes a little while until the wall is completely dried through to the core area.

There is quite a detailed information sheet on the subject "Waterproof Concrete Structures" – just google it.
And that’s why even shallow flush-mounted boxes are not a good idea. Because you quickly go below the mandatory 200mm. The installer just needs to have not removed the centering drill beforehand...

Assumption or part of the scope of work description?

Part of the scope of work description: "Concrete ceilings and walls in the basement will not be plastered (except basement 1, 2 and 3, which will also be plastered)"

I’ll try to understand the information sheet. I previously spoke with another contractor, who told me that the waterproof concrete is already completely sealed after about 3cm, since no water is allowed to penetrate the middle layer, which apparently is the load-bearing one. Therefore, he saw no problem regarding water, but if the installation of the boxes is not done highly professionally, because if cutting and chiseling are done with an angle grinder and chisel, the "structure of the wall" gets damaged.

Now, to be honest, I’m completely confused

No, I mean that only the exterior walls of the basement would be made of concrete (precast or in-situ, doesn’t matter) into which the interior walls are built. Then the cables are laid flush-mounted normally in the interior walls and you save yourself the hassle with claddings and so on

Oh, that’s how we did it too. It’s just quite unprofessional if I then have cables running across the office in the new building – so there remain several boxes that simply should be in the exterior walls...

Small update on this matter.

I have now spoken with:
- site manager
- another construction company known to me
- the Bauherren-Schutzbund

Results:
Site manager:
Due to the reduced width of the reinforced concrete wall caused by the boxes, the waterproof tank will be compromised.
So far, I have not had any negative experiences in this regard.
(This occurs to him rather late – until now it was always said that this would cause no problems at all)

Construction company known to me:
The white tank is watertight after about 3 cm – I have nothing to fear there. However, he says that the "overall structure of the wall" is affected by the cut. Normally, boxes including pipes are cast in already during concrete pouring. (exactly what we explicitly did NOT do on the advice of the site manager, while the electrician originally wanted to do it that way…)

Bauherren-Schutzbund:
"We strongly advise against subsequent flush-mounted installations in exterior walls made of WU concrete. The reasons are the weakening of the concrete thickness of the exterior wall below the required measure as well as the risk of cracks in the concrete which can occur during the subsequent chiseling and drilling work. Both factors can impair the waterproofness of the concrete."
"The possibility of a cladding shell to create an installation level depends, among other things, on the soil conditions and the type of load from pressing water or moisture from outside."
"The installation level should in any case be ventilated. The same applies regarding the connection of room ventilators as for the subsequent electrical installation on the exterior walls in general."

Now, independently of the boxes, I face the problem that the decentralized ventilators have already been cast in, but not the electrical connection for them. Here *it has to* be chiseled and broken out, unless they rebuild the house.

What do you recommend? How can I also create liability security for myself here? The site manager has now, one week before the electrical installation and due to the skepticism of the electrician (!), suddenly changed his position. However, he will have no option but to hammer into the WU concrete for the decentralized ventilators.

For the sockets, I am now reluctantly tending towards baseboard channels but I am extremely annoyed about this, especially since this apparently would not have been a problem with proper planning.

Why can't a duct be installed to the fans?